1. Technical Field
The present invention relates to an apparatus for continuous vacuum forming of a thermoplastic material between a pair of rotating belts in which the belts maintain alignment to one another.
2. Description of the Related Art
Apparatus for continuous plastic molding between belt molds are known. U.S. Pat. Nos. 4,128,369 and 4,290,248 describe an apparatus in which a thermoplastic material is introduced between traveling flexible belt molds, which revolve in opposed relationships. A sheet metal belt travels in a mold channel. A flexible three-dimensional pattern is formed in a front face of the belt. Opposed nip rolls press the revolving belt molds against the thermoplastic material. Sixty or more small diameter rolls are used to maintain the two traveling mold surfaces in close contact.
U.S. Pat. Nos. 5,167,781 and 5,458,477 describe a continuous molding apparatus in which a pair of multi-ply woven endless fabric belts have silicone rubber outer mold adhered to a respective outer side of the fabric belts. A back-up plate is coated with a low friction material over which slides the continuously moving belt mold. These patents have the limitation of loss of alignment between belts or rollers during use.
U.S. Pat. No. 5,906,840 issued to the inventors of the present disclosure describes an apparatus for continuous vacuum forming a material in which a flexible material is continuously rotatable with a flat support belt. The flexible patterned belt has a patterned section along the length thereof and a pair of raised edge sections. The flexible belt and the support belt include perforations and a vacuum is in fluid flow with the perforations of the flexible belt and the perforations of the support belt to provide alignment of the flexible belt.
It is desirable to provide an apparatus for continuous vacuum forming between a pair of rotating belts having improved alignment of the belts.
The present invention relates to an apparatus for continuous vacuum forming of a thermoplastic material between a pair of rotating flexible belts in which one belt includes a plurality of teeth, which are received in a plurality of indentations of the other belt. Each of the belts includes a mold, which forms a channel when the belts are adjacent to one another. A vacuum is applied to at least one of the flexible belts for drawing material received in the channel and alignment of the belts. Preferably, a vacuum can be applied to both of the belts for improved alignment. Each belt can include a plurality of apertures, which are in fluid flow communication with a plurality of perforations of a flat support belt positioned over a vacuum manifold.
The invention will be more fully described by reference to the following drawings.